Method and node for the control of a connection in a communication network

ABSTRACT

In a method for the control of a connection in a communication network comprising a plurality of nodes (MSC, TSN, MG), a connection (CO) is established stepwise between nodes (MSC, TSN, MG). At least two of the nodes (MSC, TSN, MG) are adapted to insert an entity into the connection (CO), the entity affecting the connection quality, or to remove an entity affecting the connection quality from the connection. An indicator is forwarded between nodes controlling the connection (CO) wherein the indicator indicates whether the connection (CO) comprises an entity affecting the connection quality. A node which decides to insert an entity into the connection or remove an entity adjusts the indicator accordingly before forwarding it to a further node (MSC, TNS, MSC′) controlling the connection (CO). A node (MSC, TSN, MSC′) controlling the connection (CO) checks the value of the indicator when it performs a decision to insert or remove an entity. Nodes and program units for performing the method are also described.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the control of a connection in acommunication network.

BACKGROUND OF THE INVENTION

Communication networks consist of interconnected nodes and can besubdivided into core networks and access networks, the latter providingaccess to user equipment, for example a wireless access for mobile userequipment to a radio access network. Core networks interconnect accessnetworks and further networks, e.g. other core networks or the Internet.In the UMTS architecture, an access network can be controlled by an RNC(radio network controller) which is connected to the core network andprovides access to the core network, i.e. serves as access node.

For the transmission on a connection, speech is encoded according to acoding scheme, alternatively denoted as codec. A coding scheme cantransport speech either in a compressed or in a non-compressed mode. Inmany networks, different coding schemes can be used and different nodescan have different capabilities for handling the coding schemes.Transcoders perform the transcoding and rate adaptations betweendifferent coding schemes. TFO (Tandem Free Operation) is a configurationof two transcoders with compatible coding schemes on the compressedvoice sides at both ends of a connection, i.e. on the interface to theuser equipment. In this case, the transcoding stages can be bypassed andthe compressed voice coding used end to end in the connection.

Out of band coding negotiation allows that speech connections areestablished end to end with a common coding scheme, i.e. the same speechcoding is used in the whole connection between the access networks. Theadvantage is that maintaining compressed voice saves core networkbandwidth and optimizes speech quality because transcoding stages areavoided.

The ITU (International Telecommunication Union) protocol BICC (bearerindependent call control) supports out of band signaling procedureswhich allow a negotiation of the coding scheme between network nodes. Inthe ITU-T proposal BICC Q.1901 (International Telecommunication Union,June 2000), coding scheme negotiation is performed from the originatingcontrol node in a connection to each subsequent node by including a listof allowed coding schemes in the APP (Application Transport Parameter)parameter in the IAM (Initial Address Message) for the set-up of theconnection. Each node checks the list and if it does not support aparticular coding type it removes it from the list. The adapted list ispassed on with the IAM and any non-supported types are removed as longas the BICC signaling is supported. When the final node, either theterminating node or the last node supporting BICC is reached, the codingscheme type with highest priority is selected. This coding scheme andthe list (reduced to an active coding scheme list) are returned to theoriginating node via all intermediate nodes.

If a transcoder selection is performed by a node at a PLMN (Public LandMobile Network) border then the indication of the selected coding schemeto subsequent nodes in the section of the connection through the PLMnetwork is a compressed voice coding scheme. In the BICC coding schemenegotiation procedures there are no rules defining how many transcoderstages are allowed and whether an access network that supports out ofband coding scheme negotiation can insert transcoders to keep TrFO(transcoder free operation) between the access node and the rest of thenetwork. The number of transcoding stages in a connection end to end canseriously affect the speech quality. If TFO is not possible, more thanthree transcoding stages typically cause substantial speech degradation.The number of stages causing a substantial degradation depends on thecoding algorithm and the speech degradation by further entities in theconnection.

The coding scheme negotiation procedures may result in transcoders beinginserted to enable supplementary services or because the bearertechnology in a node or network does not support compressed voice. Forexample, ATM (Asynchronous Transfer Mode) networks allow thetransmission of either compressed or non-compressed speech while STM(Synchronous Transfer Mode) networks require non-compressed speechcoding. Furthermore, the negotiation should result in the optimumlocation of the transcoders which is not always the case. For example,for connections exiting an STM network to ATM, a transcoder should belocated at the network edge to save bandwidth in the ATM network by useof a compressed coding scheme.

In many cases, it is necessary to modify the coding scheme in a sectionof a connection. For example, a connection is often transferred betweendifferent access networks due to a handover. Modifications in the corenetwork are disadvantageous, especially if they require increasedtransmission bandwidth which will sometimes not be available causing atermination of the connection. The transcoder number in a connection canbe increased by a modification with corresponding quality degradation.Again, an optimum location of transcoders is often not achieved.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to obviate the abovedisadvantages and enhance the average quality of connections in acommunication network. It is a further object to avoid both adeterioration of a connection due to changes in the coding scheme and tominimize impacts on the connection in the core network.

The proposed method concerns a communication network comprising aplurality of interconnected nodes. In the communication network, aconnection is established stepwise between nodes, generally with anestablishment message or a group of establishment messages. At least twoof the nodes are adapted to insert an entity into the connection whichaffects the connection quality or remove an entity affecting theconnection quality from the connection. The entity can be embodied ashardware or as software executed in a processing system of a node.

An indicator is forwarded between nodes controlling the connection,preferably until a final node controlling the connection is reached or alast node which can handle the indicator. The indicator indicateswhether an entity affecting the connection quality is present in theconnection or, if the connection is not yet completely established, inthe part of the connection already established. The indicator can forexample be sent in the establishment message. A node controlling theconnection is adapted to insert an entity into the connection or removean entity from it, optionally by control messages to other nodes. Incase that the controlling node decides an insertion or removal of atranscoder, the node adjusts the indicator accordingly before forwardingthe adjusted indicator to a further node controlling the connection.

In a decision to insert or remove an entity during the establishment ormodifications of the connection, a node controlling the connection canthen check the value of the indicator. The decision can be triggered forexample by a request modify the connection parameters from a furthernode or in the node itself, e.g. if a handover is necessary. Forexample, the result of the decision can be to add a transcoder if theindicator indicates that no transcoders are present in the connectionwhile preferably no transcoders are added if further transcoders arealready present. The removal of a transcoder is caused if a node in theconnection receives a request to modify the coding scheme in one sectionof the connection to the coding scheme which is already used in theadjacent section on the other side of said node as a preferable nodecompares the coding schemes in both adjacent sections and removesunnecessary transcoders.

The proposed method is especially adapted to out of band signaling forconnection establishment and modification. It is, however, alsoapplicable for connections with in-band signaling. In the latter case,the connection is preferably established in a first step, the presenceof entities affecting the quality and the indicator are determined in asecond step and finally modifications of the entities can be performedto achieve the desired value of the indicator.

The proposed method allows to enhance the average quality of connectionsin a communication network and avoid the deterioration of a connectiondue to changes in the coding scheme. Impacts on the connection in thecore network are minimized because many modifications can be kept localin a single node or in an adjacent pair of nodes. It is possible, toperform temporary modifications, especially when localized within anode, without sending an indicator, for example an insertion of atranscoder pair into the connection for an announcement or toneinsertion.

In a preferred embodiment, the indicator is a flag indicating whetherany entity is present in the connection. This allows a simpleimplementation of the method and a small message size.

Alternatively, the indicator can be a counter indicating the number ofentities in the connection. The indicator can also be a variableindicating the accumulated speech degradation by the entities in theconnection. For the evaluation of the indicator in the decision, acomparison to a threshold value is proposed. This allows to insert afurther transcoder even if the connection already comprises one while ahigher transcoder number or speech degradation than the threshold isexcluded. The control of the connection is improved in this way.

The entity affecting the speech quality can especially be a transcoderor a pair of transcoders. Another example is a conference device forconnecting conference calls.

Handling and control of the connection can be performed in the samenode, e.g. in a mobile services switching center according to GSMspecifications. Alternatively, the communication network can comprise aseparate control plane with control nodes and a user plane with payloadnodes which are controlled by the control nodes. Then control messages,e.g. establishment messages, comprising the indicator are sent betweencontrol nodes and the connection is set up between payload nodes.

The proposed method is especially suitable if the connection is a speechconnection.

In a modification of the connection, the insertion or removal ofentities is preferably controlled by modification messages between thenodes controlling the connection.

To provide the present value of the indicator to the nodes controllingthe connection, the indicator can be included in an establishmentmessage or modification message. Preferably, the result of all changesduring the establishment or modification of a connection, i.e. the finalvalue of the indicator, is forwarded to the nodes controlling theconnection, especially to the nodes adapted to insert or remove anentity. The indicator can be updated in an acknowledgement message for amodification message or an establishment message, respectively.

To resolve conflicts in the case of crossing modification messages, itis proposed that a defined node controlling the connection has apriority for selecting a modification. For example, either theoriginating or the final node in any connection can have the priority todiscard modifications by other nodes in this case.

A preferable node for the control of a connection in a communicationnetwork with a plurality of nodes has an interface to at least onefurther node for receiving control messages for a connection, e.g.establishment messages, modification messages or acknowledgements. Aprocessing system of the node is adapted to establish at least a sectionof the connection and insert an entity into the connection which affectsthe connection quality or remove an entity affecting the connectionquality from the connection. If the node is a control node, theseprocesses can be performed by corresponding commands to a payload node.

The processing system of the proposed node checks a received controlmessage for an indicator indicating the presence of an entity affectingthe connection quality in the connection and stores the value of theindicator in a memory. The processing system checks the present value ofthe indicator when it performs a decision to insert or remove an entity.The processing system adjusts the stored value of the indicatoraccording to the decision and forwards the value over the interface to afurther node in the connection. The node can be used in any of the abovemethods.

An advantageous program unit is stored on a data carrier or loadableinto a network node and comprises code for receiving a control messagefor a connection, e.g. an establishment message or a modificationmessage or an acknowledgement message. The program unit checks thereceived message for an indicator which indicates the presence of anentity affecting the connection quality in the connection. The unitevaluates the indicator in a decision to insert or remove an entityaffecting the quality of the connection, adapts the indicator accordingto the decision and sends it in a message to a further node whichcontrols the connection. The program unit initiates the insertion orremoval of the entity according to the decision. Functions of theprogram unit can be performed by function calls to other program units,e.g. to a processing system. The program unit can perform steps from anyof the above methods.

The foregoing and other objects, features and advantages of the presentinvention will become more apparent in the following detaileddescription of preferred embodiments as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the establishment of a first connection in a communicationnetwork

FIG. 2 shows the establishment of a second connection in a communicationnetwork

FIG. 3 shows the establishment of a connection with a transcoder on theborder between two core networks

FIG. 4 shows the establishment of a connection with a transit networkbetween two core networks

FIG. 5 shows a first alternative for the connection depicted in FIG. 1after a handover

FIG. 6 shows a second alternative for the connection depicted in FIG. 1after a handover

FIG. 7 shows a connection corresponding to FIG. 4 after a handover

FIG. 8 shows the establishment and modification of a connectionaccording to the invention

FIG. 9 shows the establishment of a connection according to a furtherembodiment of the invention

FIG. 10 shows a modification of the connection in FIG. 9 after ahandover.

FIG. 11 shows a flow diagram in a control node according to theinvention

FIG. 12 shows a flow diagram in an originating control node according tothe invention

FIG. 13 shows a legend of acronyms for use with FIGS. 1-12.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, FIGS. 1 to 4 show different examples ofconnections. FIGS. 5 to 7 depict the influences of modifications onthese connections without the proposed method while FIGS. 8 to 10illustrate the influences of modifications performed using the proposedmethod. Corresponding reference signs relate to corresponding featuresin all figures. FIG. 13 provides a legend for use with FIGS. 1-12.

FIG. 1 shows the establishment of a first connection in a communicationnetwork. The network comprises a user plane with payload nodes MG, e.g.media gateways, for the handling of the payload. At both ends, accessnodes RAN provide connections to UMTS radio access networks which handlethe wireless connections to user equipment. A control plane comprisescontrol nodes, e.g. mobile services switching centers MSC and transitnodes TSN, which control the nodes MG handling the payload. It ispossible that a control node controls several payload nodes or that apayload node is controlled by several control nodes simultaneously.

The connection establishment is initiated from an originating controlnode MSC, e.g. according to a call request received from user equipmentvia access node RAN. The connection is established stepwise using one orseveral messages sent between the control nodes controlling the nodeshandling the payload in the next sections of the connection CO. Themessages comprise a list CL of possible coding schemes for theconnection which can be selected by the receiving node. A typical codingscheme list comprises for example the schemes AMR (Adaptive MultirateCoding), EFR (Enhanced Full Rate) and PCM which is also denoted G711.The receiving node returns an acknowledgement message SC with theselected coding scheme indicated in brackets. In the example, the AMRcoding can be selected for the whole connection because all nodes arecompatible with UMTS specifications.

The connection in FIG. 1 is established between two UMTS PLMN networksCN1, CN2 as indicated by a dot-dashed line separating both. Thetransport mode in the user plane of both networks is for example ATM.When the connection is set up from access node RAN and all nodes selectAMR for the connection, this coding scheme can be used end to endbetween both radio access nodes RAN, RAN′ through both core networksCN1, CN2.

For simplicity, as in all figures, connections represented by dashedlines indicate a coding scheme with speech compression while continuouslines indicate a coding scheme without speech compression. Blackrectangles represent a transcoder TR in the respective node.

The coding scheme negotiation procedures allow a node to insert atranscoder if it cannot continue the connection establishment using acompressed voice coding scheme from the available list CL. In a secondconnection depicted in FIG. 2, the originating access node RAN is againpart of a UMTS radio access network while the receiving end is a GSMnetwork with a base station controller as access node BSC for theconnection to the core network CN2. As in FIG. 1, the AMR coding schemecan be used throughout most of the connection.

However, at the receiving end it is necessary to include a transcoder toconvert the coding scheme to the PCM type required by the base stationcontroller BSC′.

Different scenarios with a transcoder TR′, TR″ on the border between twocore networks are shown in FIGS. 3 and 4. In FIG. 3, the terminatinguser is located in a PSTN (Public Switched Telephone Network) CNF with alocal exchange LE as control node and connected to an access node SUB.In the PSTN, the selected is coding scheme is G711 while in the PLMN CN1serving the originating user, the selected coding scheme is AMR. Thisrequires the insertion of a transcoder TR′ on the border of bothnetworks. As this is the only transcoder in the connection, the speechquality is sufficient.

In the example of FIG. 4, the originating user is served by a UMTSaccess network with access node RAN while the terminating user is servedby a GSM network with access node BSC. Both networks are interconnectedby a transit network TNN which does not support the transmission ofcompressed voice but forwards an establishment message CT and transfersan acknowledgement message ST. In this case the originating end receivesAMR coding scheme while the terminating end of the connection requiresG711 coding scheme. A further transcoding is required for the transitnetwork TNN which can be for example an STM network requiring PCMcoding. Corresponding transcoders TR″ are located at the bordersindicated by dot-dashed lines between the core networks CN1, TNN, CN2.The result is that the high number of four transcoding stages results ina strong quality degradation of the connection.

It is often necessary to modify the coding scheme in a section of aconnection, e.g. if the connection is transferred between differentaccess networks due to a handover which can be required when a userleaves a coverage area of a network or if a different access network isneeded to fulfill changed connection requirements. As can be seen fromFIGS. 5 to 7 there are generally two options if a modification isnecessary for the encoding in a section of a connection.

-   -   1. A coding scheme modification can be performed and signaled,        the modification either resulting in a different compressed        voice coding scheme (<16 kb/s) or in a PCM (Pulse Code        Modulation) non-compressed coding (64 kb/s).    -   2. Two transcoders can be inserted, one to match the active        coding scheme of the section of the connection and the other to        match the new coding scheme after modification. PCM encoding        runs between the transcoders. If the transcoders are co-located        only a very short section of the transmission is performed at 64        kb/s, ideally within a node.

If the first option is performed and no transcoders are in theconnection as in the, example of FIG. 1, then the BICC coding schememodification procedures result in a transcoder inserted at the far end'saccess node. This is where the coding scheme modification procedureswill be terminated because any intermediate node receiving a codemodification message MC performs the modification and forwards themessage to the subsequent node until a node is reached which can notpass it on. Thus the entire connection through the core networks revertsto PCM with a data rate of 64 kb/s which is confirmed in anacknowledgement message MCA returned to the node which initiated themodification. The modification is often disadvantageous as morebandwidth is needed in the network and modifications are necessary inall nodes. Two transcoders are added to the connection as can be seenfrom the comparison of FIGS. 1 and 5.

If a re-negotiation of the connection with a new list of coding schemesis allowed in the network, the result can be a coding which was notnegotiated at connection establishment, e.g. the modified coding schemeis not contained in the GSM coding scheme list to support TFO. Thenthere may be a node in the connection that does not support the codingscheme. As a result it would also be necessary to use PCM across thenetwork.

The second of the above options is advantageous if the entire connectionwas originally transcoder free because only two transcoders are addedwhich are preferably located in the same access network or in an accessnode and a node adjacent to the access network requiring themodification. No modifications of other sections of the connection andin further nodes of the connection are required. Thus bandwidth is savedand also the complications avoided of inserting transcoders at the farend of the connection. This is obvious from the comparison of FIGS. 5and 6.

However the second option is not the best solution if the connection wasalready established with transcoders in other parts of the network likein FIG. 4. This results in six transcoders in the example of FIG. 7which severely affect the connection quality. In contrast, a codingscheme modification according to the first option would remove onetranscoder in the example of FIG. 4. In the example of FIG. 3, thesecond option would also increase the transcoder number.

A problem with existing connection control messages is that the nodes ina connection do not know if the connection was successfully negotiatedend to end with a single coding scheme or if a transcoder is inserted,e.g. when the connection crosses the border between networks. Theproposed method provides information to the nodes which perform codingscheme negotiation about the transcoding stages in the connection. Thenode can then optimize the establishment or modifications in theencoding of the connection both for bandwidth usage and transcodingstages, i.e. the node can select the preferable of the two optionsabove.

The method proposes a new indicator which is, e.g., added to the messagein the negotiation of the connection parameters according to BICC. Theindicator can be implemented in a number of different ways. Twoembodiments are a flag indicating whether a connection istranscoder-free from end to end or a counter containing the number oftranscoders in a connection.

It is possible that the connection is modified at two nodes, e.g. in thecase of a handover at both ends of a connection or an introduction of asupplementary service and a handover. In this case the indicator is notsufficient to achieve the desired configuration of transcoders. Forexample, nodes at both ends of a connection may add a pair oftranscoders resulting in four transcoders. This can be avoided by a CodeModification message CM sent to all control nodes in the connectioncomprising the indicator or indicating that the indicator is changed.The control nodes MSC, TSN for the access and payload nodes are in thisway always provided with the present state of the flag or counter oftranscoders in the connection.

A problem can arise in case of a crossed event when both sides modifythe connection and accordingly the indicator almost simultaneously, i.e.the indicator is not updated by the code modification message CMsufficiently fast to represent the present state of the connection. Toresolve this problem an acknowledgement MCA is proposed. Preferably, theacknowledgement MCA also comprises the present state of the indicator.One side of the connection, e.g. the originating side has a higherpriority to insert transcoders. The side with the higher priority canthen reject the change of the side with lower priority and only thelower priority side modifies the encoding.

In the first embodiment the indicator is a flag TF which indicateswhether the coding scheme negotiation for the set-up of a connection ora modification was performed end to end or terminated at an intermediatenode in the network. This provides the necessary information for thenodes in the connection, e.g. the control node for an access network, todecide if they can add one or two further transcoders in a connection.If this is the case, the access node and the adjacent payload node add apair of transcoders if the flag is not set while no transcoder or asingle transcoder is added if the flag is set. For example, in case of ahandover from a UMTS to a to GSM access network, the UMTS AMR can bekept in a PLMN as shown in FIG. 8. This saves bandwidth in the corenetwork and avoids unnecessary modifications of the connection. Anadvantage of the embodiment of the indicator as flag is that a singlebit is sufficient to represent the possible states “y” corresponding toa transcoder free connection end to end and “n” corresponding to aconnection comprising transcoders. The implementation is simple.

In the second embodiment, the indicator is a counter representing thenumber of transcoding stages which is passed between nodes duringconnection set-up and changes in the transcoding. This allows theapplication of a threshold for the number of transcoding stages that maybe inserted. More generally, the method can also be applied to avoidspeech degradation due to other equipment in the connection which affectthe speech quality. The maximum number of stages depends on the level bywhich the connection is affected in every stage. A suitable thresholdvalue is for example three transcoding stages as maximum allowed value.The threshold can also depend on the selected coding scheme in asection, e.g. the threshold may be three stages except when EFR codingis selected for which a maximum of four stages could be allowed. In athird embodiment, is also possible that instead of a counterrepresenting the number of stages, the indicator is a variable which isincreased according to the level of degradation caused by the respectivestage.

When a connection is established with BICC messages, the APP sent in theforward direction includes the indicator and the indicator isincremented if a node inserts a transcoder unit. The terminating nodereceives the indicator and determines if it can still add transcoders.If the terminating node inserts a transcoder, it also increments thecounter. From the terminating node, the counter is returned to theoriginating node in the APM (Application Transport Mechanism) along withthe selected coding scheme. The value is stored in all nodes controllingthe connection. If a modification occurs, for example due to handover,the transcoder counter is updated and sent with the APM for codingscheme modification to all control nodes for the connection.

If a network node starts the coding scheme negotiation for a connectionfrom a network in which the transcoder counter is not supported (e.g. inwhich BICC is not supported or in which a flag instead of a transcodercounter is used) preferably a default value is set corresponding to anunknown number of transcoding stages.

FIG. 9 depicts the set-up of a connection in a communication network asdescribed with respect to FIG. 4. The originating MSC has received AMRas selected coding scheme in message SC, and thus compressed speech isused across the core network CN1. In this case, the transit network TNNis adapted to forward the indicator, i.e. transcoder counter TN, in amessage CT and in the corresponding acknowledgement ST. Therefore, allcontrol nodes in the connection are provided by the acknowledgementmessages SC, SC′, ST with the information that two transcoders arelinked into the connection.

In FIG. 10, a handover HO for this connection is performed from a UMTSaccess node RAN to a GSM access node BSC. The anchor node MSC for thehandover HO has stored the counter indicating that the connectionalready has two transcoders in it. If two further transcoders are addedin the access section of the connection then the threshold for thenumber of transcoders will be exceeded. Therefore, a single transcoderis added in the access node BSC as required by the handover resulting ina present transcoder number of three in the connection. The decision isthen made in the control node MSC to modify the coding scheme to PCMwhich generally reduces the number of transcoders in a connection to amaximum of two because all nodes in the core networks can handle the PCMcoding scheme. The information is passed on to the next control node inthe code modify message MC with the present counter value of three. Themessage to modify to the PCM coding scheme, which is already used in onesection of the connection adjacent to payload node MG′, also in theother section adjacent to payload node MG′ allows the control node TSNto remove the transcoder unit at the network border. The updatedtranscoder counter TN of two is then returned to the control node MSC inthe acknowledgement MCA. Preferably, the updated transcoder counter TNis also forwarded to the further control nodes TSN′, MSC′ in theconnection with messages MCA′, MCA″.

The same decision can also be performed if the counter is not supportedby the transit network and set to a default value by the transit nodeTSN. Then the anchor MSC performs the same decision based on the factthat an unknown number of transcoders is present in the connection.

Both in the case of FIG. 9 and FIG. 10, the first control node MSC couldreceive a high transcoder number in the acknowledgement messages SC,MCA, depending on the selections of the other control nodes TSN, TSN′,MSC′ in the connection and the network architecture. In this case, thefirst control node MSC can modify the connection with a further codemodify message to reduce the transcoder number.

FIG. 11 depicts an example of a flow diagram for the decision to inserta transcoder in a terminating or transit control node MSC, TSN for aconnection, e.g. in a node receiving an establishment message 2. In themessage 2, the control node receives a list CL with allowed codingschemes and the counter TC with the transcoder number in the connection.The node checks if all coding schemes in the list CL are supported andremoves unsupported schemes in step 4. Then a check 6 is performedwhether a transcoder is needed or preferable, e.g. because the node islocated at a boundary between core networks or to an access network withdifferent transport protocols.

If the result of check 6 is that a transcoder should be inserted,counter TC is incremented in step 8 and a comparison 10 of thetranscoder counter with a predefined threshold for the maximum number oftranscoders is performed. If the result of comparison 10 is that thetranscoder number is equal to or larger than the threshold, G711 isselected as coding scheme in step 12 and the transcoder counterdecremented. Then a further check 14 is performed whether the node isthe terminating node controlling the connection or a transit node. Incase of a transit node, the list CL of allowed coding schemes is reducedto G711 in step 16. The reduced list CL consisting only of G711 as onlyallowed coding scheme is forwarded together with the updated transcodercounter TC to the next control node for the connection in a furtherestablishment message 18.

The result of check 14 can also be that the control node is aterminating node, e.g. the last control node before the terminatingaccess network in the connection. Then a transmission of the selectedcoding scheme, i.e. G711, together with the transcoder number isperformed to the originating node of the connection via all previoustransit nodes in a message 20.

If no transcoder is needed as determined in check 6 or if the transcodernumber is below the threshold as determined in check 10, then also acheck 22 is performed whether the node is the terminating nodecontrolling the connection. For a terminating node, a selection 24 of acoding scheme from list CL is performed. An insertion 26 of one or apair of transcoders is performed if a transcoding is required asdetermined in check 6. The selected coding scheme from check 22 and thefinal value of the transcoder counter TC is returned in a message 20 tothe originating node via all previous transit nodes.

For a transit node according to check 22, the adjusted list CL of codingschemes and the value of the transcoder counter TC is forwarded to thenext control node for the connection in a message 18. Preferably, theinsertion of transcoders into the connection is performed according tothe selected coding scheme in an acknowledgement message which isreceived in reply to message 18.

FIG. 12 depicts a corresponding flow diagram for an originating controlnode in a connection. In a first step 40, the transcoder counter TC isset to zero. Then a decision 42 is performed whether a transcoder isneeded or preferable, e.g. because the local insertion of a transcoderavoids the modification of the transcoding in a further section of theconnection. If the decision 42 is to insert a transcoder, the counter isincremented in step 44. A list CL of allowed coding schemes is definedin step 46, depending on the capabilities of the originating node.Finally, a message 48 comprising list CL and the value of counter TC isforwarded in a message to the next control node for the connection.Depending on the implementation, the insertion of a transcoder can forexample be performed in step 44 or when an acknowledgement in reply tomessage 48 is received with a selected coding scheme from the list CL.

The proposed method allows nodes to optimize the insertion oftranscoders, especially when out of band coding scheme negotiationmechanisms are used. The above embodiments admirably achieve the objectsof the invention. However, it will be appreciated that departures can bemade by those skilled in the art without departing from the scope of theinvention which is limited only by the claims.

1. Method for the control of a connection in a communication networkcomprising a plurality of nodes, wherein a connection is establishedstepwise between nodes and at least two of the nodes insert an entityinto the connection, the entity affecting the connection quality, or toremove an entity affecting the connection quality from the connection,comprising the steps of: an indicator is forwarded between nodescontrolling the connection wherein the indicator indicates whether theconnection comprises an entity affecting the connection quality, a nodewhich decides to insert an entity into the connection or remove anentity adjusts the indicator accordingly before forwarding it to afurther node controlling the connection, and a node controlling theconnection checks the value of the indicator when it performs a decisionto insert or remove an entity.
 2. Method according to claim 1, whereinthe indicator is a flag indicating whether any entity is present in theconnection.
 3. Method according to claim 1, wherein the indicator is acounter indicating the number of entities in the connection.
 4. Methodaccording to claim 1, wherein the indicator is a variable indicating theaccumulated speech degradation by the entity in the connection. 5.Method according to claim 3, wherein the indicator is compared to athreshold value in the decision.
 6. Method according to claim 1 whereinan entity is a transcoder or a conference device.
 7. Method according toclaim 1, wherein the communication network comprises control nodes andpayload nodes which are controlled by the control nodes, wherein theindicator is sent between said control nodes and the connection isestablished between said payload nodes.
 8. Method according to claim 1,wherein the connection is a speech connection.
 9. Method according claim1, wherein an entity is inserted or removed according to a modificationmessage.
 10. Method according to claim 1, wherein the indicator is sentwith an establishment message for the connection.
 11. Method accordingto claim 1, wherein a final value of the indicator after theestablishment or modification of the connection is forwarded to nodes inthe connection which insert or remove an entity.
 12. Method according toclaim 1, wherein a defined node controlling the connection has apriority for selecting a modification.
 13. A method for controlling aconnection within a communication network including a plurality of nodeswherein said connection is established between two or more saidplurality of nodes and wherein at least two of said nodes insert orremove an entity into said connection, said entity effecting the qualityof said connection, comprising the steps of; receiving a control messagefor establishing a connection; checking an indicator within said controlmessage wherein said indicator indicates whether an entity affecting theconnection quality is present in said connection; determining whether toinsert or remove an entity from said connection based on said indicator;modifying said indicator according to said step of determining;transmitting said modified indicator in a control message to a furthernode in said connection; and initiating the insertion or removal of saidentity in accordance with said step of determining.
 14. The method ofclaim 13 wherein said indicator is a flag indicating whether any entityis present in said connection.
 15. The method of claim 13 wherein saidindicator is a variable indicating the accumulated speech degradation bythe entity in said connection.
 16. The method of claim 13 wherein saidindicator is a counter indicating the number of entities present in saidconnection.
 17. The method of claim 16 wherein said step of determiningfurther comprises the step of comparing said indicator to a thresholdvalue.
 18. The method of claim 13 wherein said entity is a transcoder.19. A system for controlling a connection within a communication networkincluding a plurality of nodes wherein said connection is establishedbetween two or more said plurality of nodes and wherein at least two ofsaid nodes insert or remove an entity into said connection, said entityeffecting the quality of said connection, comprising; means forreceiving a control message for establishing a connection wherein saidcontrol message includes an indicator; means for checking said indicatorwherein said indicator indicates whether an entity affecting theconnection quality is present in said connection; means for determiningwhether to insert or remove an entity from said connection based on saidindicator; means for modifying said indicator according to saiddetermination; means for transmitting said modified indicator in acontrol message to a further node in said connection; and means forinitiating the insertion or removal of said entity in accordance withsaid determination.
 20. The system of claim 19 wherein said indicator isa flag indicating whether any entity is present in said connection. 21.The system of claim 19 wherein said indicator is a variable indicatingthe accumulated speech degradation by the entity in said connection. 22.The system of claim 19 wherein said indicator is a counter indicatingthe number of entities present in said connection.
 23. The system ofclaim 22 further storing a threshold value and said means fordetermining compares said indicator to said threshold value for makingthat determination.
 24. The system of claim 19 wherein said entity is atranscoder.